Fat is a desirable component of most animal diets, and the art is replete with methods of introducing it into the diets of various livestock. In addition to serving as an energy source, fat can have an impact on the quality and quantity of milk production in dairy animals and meat production of animals raised for slaughter, e.g. various ruminants, pigs and poultry.
Animal feed particles are generally a convenient form for use in supplementing pelleted livestock feed with, for example, additional fat and can be made using extrusion methods. In extrusion, desired ingredients to be incorporated into the feed may be mixed, cooked, sheared, gelatinized, formed and chopped into particles. The particles may also be subjected to additional coating after extrusion. Fat, for example, may be applied after the forming process by spray drums or mixers. With respect to fat, there have been limits to the amount of fat that can be incorporated prior to extrusion and also after extrusion. Incorporation of high amounts of fat results in undesirable crumbling while similar amounts applied onto the surface of the pellet or nugget produces a product that is soft, friable and has a greasy texture. The amount and type of fat can also affect the palatability of the feed particles and lead to decreased intake. Inappropriate amount and types of fat can also affect the digestibility and lead to sick cows. Dairy cows, for example, have been fed extruded particles with about 40% beef tallow. These feed particles will be referred to herein as “40% fat particles”.
Other methods to increase the fat content include a process of applying fat containing liquid to a granulated product by combining the fat containing liquid and the granulated product and generating a negative pressure in the container and then slowly releasing the negative pressure while mixing the granulated product moistened with the fat containing liquid. This method results in conveying some of the fat containing liquid into the product; however, the absorptivity of fat by the product was still relatively small.